I no longer run a guild and therefore have no need for WoW Roster. However, I would like to still be able to generate signatures/avatars for my characters and for my friends to be able to do the same if they so wish.

Is this at all possible please? If so, how? Is there a version of WoW roster and SigGen that allows guildless players to upload?

Um, is 'public roster' a completely different roster to the standard, or is it a feature of wow roster now? Its been a long time since I've tinkered with roster, its come on leaps and bounds since then!

Public roster is a mod of the base roster. However, I think the last functional release is based on 1.7.1, which is pre-tbc. You're best off waiting till siggen is proted for 2.0, since 2.0 has native multiguild/guildless capabilities.